The present invention relates to fuses, and more particularly to a modular design for an under oil expulsion fuse cartridge.
Under oil expulsion fuses are generally used in high voltage systems to protect the electrical devices from fault currents. The expulsion fuse can be used by itself or in tandem with back up current limiting fuses since it can be used to provide current interruption under low fault conditions without operation of the more costly limiting fuse.
State of the art expulsion fuse cartridges are typically manufactured by assemblying two brass end contacts such that their projecting annular lips surround opposite ends of a molded nylon sleeve, winding a glass filament epoxy strengthening layer over the nylon sleeve and projecting lips, and then coating the epoxy layer with an arc extinguishing material such as polyester until the outer surface of the polyester is flush with the outer surface of the brass end contacts.
One problem with such an assembly is that the interface between the molded nylon sleeve and the glass epoxy layer may be a problem area if there is insufficient bond between these two materials. If not bonded properly, or if the molded sleeve contracts away from the glass layer, the interface area may produce a site for corona and possible flashover between the end contacts. Another problem with such an assembly is that when the cartridge is inserted or removed from a holder assembly the holder assembly contacts are dragged across the end contacts of the cartridge and deposit small metal and/or carbon particles on the polyester layer of the housing. This build-up of particles may cause arcing and possible flashover between the end contacts during operation with the resultant arc heat burning or carbonizing the housing thus reducing the electrical dielectric efficiency of the device.